1. Embedded Systems Welcome to Lectures 7-8-9, 22-Jan-2011
IC by Dr. P P Das

2. Chapter 1: Introduction
Source: Vahid’s Website
IC 80010

3. Outline Embedded systems overview
What are they?
Design challenge – optimizing design metrics
Technologies
Processor technologies
IC technologies
Design technologies

4. Embedded systems overview
Computing systems are everywhere
Most of us think of “desktop” computers
PC’s
Laptops
Mainframes
Servers
But there’s another type of computing system
Far more common...

5. Embedded systems overview
Embedded computing systems
Computing systems embedded within electronic devices
Hard to define. Nearly any computing system other than a desktop computer
Billions of units produced yearly, versus millions of desktop units
Perhaps 50 per household and per automobile
Computers are in here...
and here...
and even here...
Lots more of these, though they cost a lot less each.

6. A “short list” of embedded systems
Anti-lock brakes
Auto-focus cameras
Automatic teller machines
Automatic toll systems
Automatic transmission
Avionic systems
Battery chargers
Camcorders
Cell phones
Cell-phone base stations
Cordless phones
Cruise control
Curbside check-in systems
Digital cameras
Disk drives
Electronic card readers
Electronic instruments
Electronic toys/games
Factory control
Fax machines
Fingerprint identifiers
Home security systems
Life-support systems
Medical testing systems
Modems
MPEG decoders
Network cards
Network switches/routers
On-board navigation
Pagers
Photocopiers
Point-of-sale systems
Portable video games
Printers
Satellite phones
Scanners
Smart ovens/dishwashers
Speech recognizers
Stereo systems
Teleconferencing systems
Televisions
Temperature controllers
Theft tracking systems
TV set-top boxes
VCR’s, DVD players
Video game consoles
Video phones
Washers and dryers
And the list goes on and on

7. Some common characteristics of embedded systems
Single-functioned
Executes a single program, repeatedly
Tightly-constrained
Low cost, low power, small, fast, etc.
Reactive and real-time
Continually reacts to changes in the system’s environment
Must compute certain results in real-time without delay

8. An embedded system example -- a digital camera
Microcontroller
CCD preprocessor
Pixel coprocessor
A2D
D2A
JPEG codec
DMA controller
Memory controller
ISA bus interface
UART
LCD ctrl
Display ctrl
Multiplier/Accum
Digital camera chip
lens
CCD
Single-functioned -- always a digital camera
Tightly-constrained -- Low cost, low power, small, fast
Reactive and real-time -- only to a small extent

9. Design challenge – optimizing design metrics
Obvious design goal:
Construct an implementation with desired functionality
Key design challenge:
Simultaneously optimize numerous design metrics
Design metric
A measurable feature of a system’s implementation
Optimizing design metrics is a key challenge

10. Design challenge – optimizing design metrics
Common metrics
Unit cost: the monetary cost of manufacturing each copy of the system, excluding NRE cost
NRE cost (Non-Recurring Engineering cost): The one-time monetary cost of designing the system
Size: the physical space required by the system
Performance: the execution time or throughput of the system
Power: the amount of power consumed by the system
Flexibility: the ability to change the functionality of the system without incurring heavy NRE cost

11. Design challenge – optimizing design metrics
Common metrics (continued)
Time-to-prototype (TTP): the time needed to build a working version of the system
Time-to-market (TTM): the time required to develop a system to the point that it can be released and sold to customers
Maintainability: the ability to modify the system after its initial release
Correctness, safety, many more

12. Design metric competition -- improving one may worsen others
Expertise with both software and hardware is needed to optimize design metrics
Not just a hardware or software expert, as is common
A designer must be comfortable with various technologies in order to choose the best for a given application and constraints
Size
Performance
Power
NRE cost
Microcontroller
CCD preprocessor
Pixel coprocessor
A2D
D2A
JPEG codec
DMA controller
Memory controller
ISA bus interface
UART
LCD ctrl
Display ctrl
Multiplier/Accum
Digital camera chip
lens
CCD
Hardware
Software

13. Time-to-market: a demanding design metric
Time required to develop a product to the point it can be sold to customers
Market window
Period during which the product would have highest sales
Average time-to-market constraint is about 8 months
Delays can be costly
Revenues ($)
Time (months)

14. Losses due to delayed market entry
Simplified revenue model
Product life = 2W, peak at W
Time of market entry defines a triangle, representing market penetration
Triangle area equals revenue
Loss
The difference between the on-time and delayed triangle areas
On-time Delayed
entry entry
Peak revenue
Peak revenue from delayed entry
Market rise
Market fall W 2W
Time D
On-time
Delayed
Revenues ($)

15. Losses due to delayed market entry (cont.)
Area = 1/2 * base * height
On-time = 1/2 * 2W * W
Delayed = 1/2 * (W-D+W)*(W-D)
Percentage revenue loss = (D(3W-D)/2W2)*100%
Try some examples
On-time Delayed
entry entry
Peak revenue
Peak revenue from delayed entry
Market rise
Market fall W 2W
Time D
On-time
Delayed
Revenues ($)
Lifetime 2W=52 wks, delay D=4 wks
(4*(3*26 –4)/2*26^2) = 22%
Lifetime 2W=52 wks, delay D=10 wks
(10*(3*26 –10)/2*26^2) = 50%
Delays are costly!

16. NRE and unit cost metrics
Costs:
Unit cost: the monetary cost of manufacturing each copy of the system, excluding NRE cost
NRE cost (Non-Recurring Engineering cost): The one-time monetary cost of designing the system
total cost = NRE cost unit cost * # of units
per-product cost = total cost / # of units
= (NRE cost / # of units) + unit cost
Example
NRE=$2000, unit=$100
For 10 units
total cost = $ *$100 = $3000
per-product cost = $2000/10 + $100 = $300
Amortizing NRE cost over the units results in an additional $200 per unit

17. NRE and unit cost metrics
Compare technologies by costs -- best depends on quantity
Technology A: NRE=$2,000, unit=$100
Technology B: NRE=$30,000, unit=$30
Technology C: NRE=$100,000, unit=$2
But, must also consider time-to-market

18. The performance design metric
Widely-used measure of system, widely-abused
Clock frequency, instructions per second – not good measures
Digital camera example – a user cares about how fast it processes images, not clock speed or instructions per second
Latency (response time)
Time between task start and end
e.g., Camera’s A and B process images in 0.25 seconds
Throughput
Tasks per second, e.g. Camera A processes 4 images per second
Throughput can be more than latency seems to imply due to concurrency, e.g. Camera B may process 8 images per second (by capturing a new image while previous image is being stored).
Speedup of B over S = B’s performance / A’s performance
Throughput speedup = 8/4 = 2

19. Three key embedded system technologies
Technology
A manner of accomplishing a task, especially using technical processes, methods, or knowledge
Three key technologies for embedded systems
Processor technology
IC technology
Design technology

20. Application-specific
Processor technology
The architecture of the computation engine used to implement a system’s desired functionality
Processor does not have to be programmable
“Processor” not equal to general-purpose processor
Controller
Datapath
Controller
Datapath
Controller
Datapath
Control
logic and State register
Register
file
Control logic and State register
Registers
Control
logic
index
total
Custom
ALU
State register +
General
ALU IR PC IR PC
Data
memory
Data
memory
Program memory
Data
memory
Program memory
Assembly code for:
total = 0
for i =1 to …
Assembly code for:
total = 0
for i =1 to …
General-purpose (“software”)
Application-specific
Single-purpose (“hardware”)

21. Processor technology
Processors vary in their customization for the problem at hand
total = 0
for i = 1 to N loop
total += M[i]
end loop
Desired functionality
General-purpose processor
Application-specific processor
Single-purpose processor

22. An embedded system example -- a digital camera
Microcontroller
CCD preprocessor
Pixel coprocessor
A2D
D2A
JPEG codec
DMA controller
Memory controller
ISA bus interface
UART
LCD ctrl
Display ctrl
Multiplier/Accum
Digital camera chip
lens
CCD
Microcontroller: General-Purpose Processor
CCD / Pixel Processor: Application Specific Processor
JPEG Codec: Single-Purpose Processor

23. General-purpose processors
Programmable device used in a variety of applications
Also known as “microprocessor”
Features
Program memory
General datapath with large register file and general ALU
User benefits
Low time-to-market and NRE costs
High flexibility
“Pentium” the most well-known, but there are hundreds of others IR PC
Register
file
General
ALU
Datapath
Controller
Program memory
Assembly code for:
total = 0
for i =1 to …
Control
logic and State register
Data
memory

24. Single-purpose processors
Digital circuit designed to execute exactly one program
a.k.a. coprocessor, accelerator or peripheral
Features
Contains only the components needed to execute a single program
No program memory
Benefits
Fast
Low power
Small size
Datapath
Controller
Control logic
State register
Data
memory
index
total +

25. Application-specific processors
Programmable processor optimized for a particular class of applications having common characteristics
Compromise between general-purpose and single-purpose processors
Features
Program memory
Optimized datapath
Special functional units
Benefits
Some flexibility, good performance, size and power
Controller
Datapath
Control
logic and State register
Registers
Custom
ALU IR PC
Data
memory
Program memory
Assembly code for:
total = 0
for i =1 to …

26. IC technology
The manner in which a digital (gate-level) implementation is mapped onto an IC
IC: Integrated circuit, or “chip”
IC technologies differ in their customization to a design
IC’s consist of numerous layers (perhaps 10 or more)
IC technologies differ with respect to who builds each layer and when
source
drain
channel
oxide
gate
Silicon substrate
IC package IC

27. IC technology Three types of IC technologies Full-custom/VLSI
Semi-custom ASIC (gate array and standard cell)
PLD (Programmable Logic Device)

28. Full-custom/VLSI
All layers are optimized for an embedded system’s particular digital implementation
Placing transistors
Sizing transistors
Routing wires
Benefits
Excellent performance, small size, low power
Drawbacks
High NRE cost (e.g., $300k), long time-to-market

29. Semi-custom Lower layers are fully or partially built Benefits
Designers are left with routing of wires and maybe placing some blocks
Benefits
Good performance, good size, less NRE cost than a full-custom implementation (perhaps $10k to $100k)
Drawbacks
Still require weeks to months to develop

30. PLD (Programmable Logic Device)
All layers already exist
Designers can purchase an IC
Connections on the IC are either created or destroyed to implement desired functionality
Field-Programmable Gate Array (FPGA) very popular
Benefits
Low NRE costs, almost instant IC availability
Drawbacks
Bigger, expensive (perhaps $30 per unit), power hungry, slower

31. Moore’s law The most important trend in embedded systems
Predicted in 1965 by Intel co-founder Gordon Moore
IC transistor capacity has doubled roughly every 18 months for the past several decades
10,000
1,000
100 10 1
0.1
0.01
0.001
Logic transistors per chip
(in millions)
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
2009
Note: logarithmic scale

32. Moore’s law
Wow
This growth rate is hard to imagine, most people underestimate
How many ancestors do you have from 20 generations ago
i.e., roughly how many people alive in the 1500’s did it take to make you?
220 = more than 1 million people
(This underestimation is the key to pyramid schemes!)

33. Graphical illustration of Moore’s law
1981
1984
1987
1990
1993
1996
1999
2002
10,000
transistors
150,000,000
transistors
Leading edge
chip in 1981
Leading edge
chip in 2002
Something that doubles frequently grows more quickly than most people realize!
A 2002 chip can hold about 15, chips inside itself

34. Design Technology
The manner in which we convert our concept of desired system functionality into an implementation
Libraries/IP: Incorporates pre-designed implementation from lower abstraction level into higher level.
System
specification
Behavioral RT
Logic
To final implementation
Compilation/Synthesis: Automates exploration and insertion of implementation details for lower level.
Test/Verification: Ensures correct functionality at each level, thus reducing costly iterations between levels.
Compilation/
Synthesis
Libraries/ IP
Test/
Verification
synthesis
Behavior
Hw/Sw/ OS
Cores
components
Gates/
Cells
Model simulat./
checkers
Hw-Sw
cosimulators
HDL simulators
Gate
simulators

35. Design productivity exponential increase
100,000
10,000
1,000
100
(K) Trans./Staff – Mo.
Productivity 10 1
0.1
0.01
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
2009
Exponential increase over the past few decades

36. The co-design ladder In the past: Hardware/software “codesign”
Hardware and software design technologies were very different
Recent maturation of synthesis enables a unified view of hardware and software
Hardware/software “codesign”
Implementation
Assembly instructions
Machine instructions
Register transfers
Compilers
(1960's,1970's)
Assemblers, linkers
(1950's, 1960's)
Behavioral synthesis
(1990's)
RT synthesis
(1980's, 1990's)
Logic synthesis
(1970's, 1980's)
Microprocessor plus program bits: “software”
VLSI, ASIC, or PLD implementation: “hardware”
Logic gates
Logic equations / FSM's
Sequential program code (e.g., C, VHDL)
The choice of hardware versus software for a particular function is simply a tradeoff among various design metrics, like performance, power, size, NRE cost, and especially flexibility; there is no fundamental difference between what hardware or software can implement.

37. Independence of processor and IC technologies
Basic tradeoff
General vs. custom
With respect to processor technology or IC technology
The two technologies are independent
General-purpose
processor
ASIP
Single-
purpose
Semi-custom
PLD
Full-custom
General,
providing improved:
Customized,
Power efficiency
Performance
Size
Cost (high volume)
Flexibility
Maintainability
NRE cost
Time- to-prototype
Time-to-market
Cost (low volume)

38. Design productivity gap
While designer productivity has grown at an impressive rate over the past decades, the rate of improvement has not kept pace with chip capacity
10,000
1,000
100 10 1
0.1
0.01
0.001
Logic transistors per chip
(in millions)
100,000
1000
Productivity
(K) Trans./Staff-Mo.
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
2009
IC capacity
productivity
Gap

39. Design productivity gap
1981 leading edge chip required 100 designer months
10,000 transistors / 100 transistors/month
2002 leading edge chip requires 30,000 designer months
150,000,000 / transistors/month
Designer cost increase from $1M to $300M
10,000
1,000
100 10 1
0.1
0.01
0.001
Logic transistors per chip
(in millions)
100,000
1000
Productivity
(K) Trans./Staff-Mo.
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
2009
IC capacity
productivity
Gap

40. The mythical man-month
The situation is even worse than the productivity gap indicates
In theory, adding designers to team reduces project completion time
In reality, productivity per designer decreases due to complexities of team management and communication
In the software community, known as “the mythical man-month” (Brooks 1975)
At some point, can actually lengthen project completion time! (“Too many cooks”) 10 20 30 40
10000
20000
30000
40000
50000
60000 43 24 19 16 15 18 23
Team
Individual
Months until completion
Number of designers
1M transistors, 1 designer=5000 trans/month
Each additional designer reduces for 100 trans/month
So 2 designers produce 4900 trans/month each

41. Summary Embedded systems are everywhere
Key challenge: optimization of design metrics
Design metrics compete with one another
A unified view of hardware and software is necessary to improve productivity
Three key technologies
Processor: general-purpose, application-specific, single-purpose
IC: Full-custom, semi-custom, PLD
Design: Compilation/synthesis, libraries/IP, test/verification